Reactions of sodium with hydrocarbons



Patented Sept. 15, 1936 PATENT OFFICE 2.054.303 REACTIONS OF SODIUM WITH HYDBOOA Norman D. Scott, Banborn, N. Y., assignor to E. I.

du Pont de Nemours as Company, Wllmingto RBONS Del., a corporation of Delaware No Drawinl.

This invention relates to improvements in the method of effecting the reaction of alkali metals with aromatic hydrocarbons, and more specifical- 1y to a method of eflfecting addition of alkali met- 5 als to naphthalene and its homologues. This application is a division of my co-pending application, Serial No. 678,261, filed June 29, 1933.

It is well known that alkali metals will react with a wide variety of aromatic hydrocarbons under a wide variety of conditions. An extensive review of this work has been published by C. B. Wooster (Chemical Reviews XI 1 Aug. 1932). While most of the reactions described are at present of little technical significance on account of the cost of the materials involved, there is particular interest in the attempts that have been made to react alkali metals with the cheaper hydrocarbons such as naphthalene. Schlenk (Annalen 463 90-95) carried out slow reactions using lithium in ethyl ether and obtained sufilcient reaction in eight days with naphthalene, and in fourteen days with diphenyl, to permit some examination of the products formed. He represented the alkali metal compounds by the formulae,

Schlenk, using ethyl ether as solvent, failed to get any detect ble reaction of sodium with these hydrocarbons even in months. He attributed this toia' poisoning effect on the sodium of minute traces of sulfur compounds present even in the by immediate ammonclysis of three atoms of the sodium to sodamide as represented by the equations:

55 Because of the large consumption of sodium and ing application,

matured into Patent 2,027,000 Jan. '7, 1936, I have best grades of naphthalene as supplied for a dium to one molecule of naphthalene, followed,

Original application June 29, 1933, Serial No. 678,261. Divided tion November 8, 1935, Serial No. 48,896

2 Claims. (Cl. 260-168) and this applicathe reactivity of the ammonia used as solvent, this method is practically useless as a means of preparing acids or other derivatives from naphthalene.

An object of this invention is to provide a method for causing alkali metals, and specifically sodium to be added to naphthalene or its homologues; a further object is to cause this reaction to be carried out at temperatures and under conditions favorable to the stability of the products; a further object is to provide a rapid reaction; my invention also includes the product or products formed by the addition of sodium and potassium to naphthalene or its homologues. Other objects will appear from the description of the invention. -I have found that certain solvents and classes of solvents have a very specific action in promoting the reaction of alkali metals with naphthalene to form addition products. As stated, the action of these solvents is specific, but I do not know whether their action is catalytic, whether the solvent itself takes part in the reaction in some manner, or whether there are some solubility or other physical factors involved.

The solvents which I have found of such remarkable activity and usefulness for these reactions are broadly in the class of ethers although all of the ethers are not efiective, and of the effective ones, some are better than others. Thus although only a few mono ethers are satisfactory as described and claimed in my co-pend- Serial No. 638,524, which has used satisfactorily aliphatic poly ethers of all types. By poly ethers in this case I mean the fully alkylated products of polyhydric alcohols such as the glycols and glycerols and including the ethers from the hypothetical polyhydric alcohols such as methylene glycol or others with more than one hydroxyl group on the same carbon atom, e. g. ethyl ortho formate, methylal or other acetals. Thus I have used successfully methylal; ethylene glycol diethers such as the methyl methyl, methyl ethyl, ethyl ethyl, methyl butyl, ethyl butyl, butyl butyl, butyl lauryl; trimethylene glycol dimethyl ether; glycerol trimethyl ether; glycerol dimethyl ethyl ether; methyl ortho formate; ethyl ortho formate; diethylene glycol methyl ethyl ether; formal of the monomethyl ether of ethylene glycol',cyclic ethers such as dioxane, glycol formal, methyl glycerol formal; dimethylene pentaerythrite; and the like. In the case of ethers of the poly alcohols such as the glycerols they may have the O on adjacent C atoms as in ethylene glycol or 1.2 Pr pylene glycol or they may be separated as in 1,3 propylene glycol.

The chief requirement of these poly others is that they must not react with the alkali metal or the alkali metal addition compounds under the conditions used. I do not mean by this that the ethers may not react in some way in some reversible reaction with the alkali metal and/or naphthalene since indications are that the ethers in ell'ecting the reactions may to some extent take part in the reaction, but the ether must not be broken up or form irreversible reaction products at a rate comparable with the desired reactions. A slight irreversible reaction may take place without a substantial loss. In order to simplify the wording later, I further specify such ethers as are effective within my invention as being inert, although as noted they may play some active role in causing the reactions to proceed, or may undergo decomposition reactions at rates very slow in comparison with the desired addition reactions.

I have found that inert non-ether types of solvents such as hydrocarbons or alkyl sulfides which do not react with the alkali metals and which in themselves are 'non-eflective for the reactions may be used as diluting agents for the eil'ective aliphatic poly ethers. There is, however, a minimum concentration of the effective ether in the non-eflective solvents beyond which the reaction will not proceed. Thus. in general the eifective dimethyl ethylene glycol ether can be diluted with a non-reactive, non-eifective hydrocarbon up to 4 or 5 times its volume. If the dilution beas high as 6 or 8 times the volume of the active ether the reaction will not proceed. With the higher-mono ethers, which are noneifective or relatively non-eifective in themselves, the dilution may be greater.

- I have discovered that alkali metals can be added not only to naphthalene but to various homologues of naphthalene by the method of my invention. For further description, the invention will be illustrated particularly with respect to the reaction of naphthalene with sodium, but it is to be understood that what is said thereon will apply equally well to the reaction of the other alkali metals and to-any of the naphthalene substitution products capable of forming addition compounds with alkali metals.

- I have found that sodium reacts very readily with naphthalene in dimethyl ethylene glycol ether solution even at 70 C. Naphthalene also reacts readily with sodium using methyl ethyl glycol ether as solvent. Other mixed poly ethers with higher primary alkyl groups can also be used, as listed above.

It is to be understood also that this invention includes the use as solvent, not only of the "effective solvents as defined and illustrated, but also of mixtures of these solvents with other solvents which may include the less active higher mono ethers, and also hydrocarbons. Considerably greater dilution with inert solvents is permissible after the reaction is definitely started.

I have further discovered that 'a solution of naphthalene in an eflective ether will readily dissolve sodium in an amount equivalent to one gram atom of sodium for each gram molecule of naphthalene; thereafter the solution of further .amounts of sodium becomes so slow as to be negligible. This is somewhat unexpected since the reaction products obtained by further treatment of the sodium-naphthalene compound, for

example, with water or CO: indicate that it is in large part the 1:4 disodium naphthalene:

HNa

conducts an electric current, it is possible that v the compound may exist in solution as a free radical which may be represented by the formula:

The soluble addition compound may involve the combination of disodium naphthalene with an extra molecule of naphthalene in some other manner. Thus its formula could be written:

NarCroHeCmHs without specifying the exact method of combination. Moreover this soluble addition product may conceivably also include some combination with the ether solvent to account for the specific action of the eflective aliphatic poly ethers. The reactions of this material, however, are clearly evident and I do not desire to be limited by any hypothesis as to the probable structure in solution.

If such a solution which contains sodium equivalent to one gram atom of sodium for each gram molecule of naphthalene be treated with water or alcohol, it will yield equivalent amounts of naphthalene and dihydronaphthalene; with CO: it will yield the sodium salts of dihydronaphthalene-diearboxy acids, along with an equivalent amount of naphthalene. If, however, either the hydrolysis or the carboxylation is carried out gradually while further amounts of sodium are present in the liquid, further amounts of this sodium will dissolve as that in the solution is used by the hydrolysis or carboxylation. In this manner I have been able to react essentially all of the naphthalene and recover the major amount as the dihydronaphthalene or dihydronaphthalene-dicarboxy acids.

As indicated above, I have made this addition of sodium to naphthalene itself and to its homologues such as alpha and beta methyl naphthalene. I have found that in the case of naphthalene itself, the product formed is in large part the 1:4 disodium compound. Formation of this compound is probably permitted by the splitting of the double bonds between the- 1:2 and 3:4 positions'and the formation of a double bond between the 2:3 positions with the sodium occupying the free linkages thus created. Such a mechanism would permit addition in a'similar manner in the case of substituted naphthalene where the 1:4 positions may be occupied by constituent groups since the reaction is not dependent on replacement of hydrogen or substituents by the sodium; there is no hydrogen evolved in the reaction of my invention as far as! have been able to discover.

I have discovered that this sodiumnaphthalene addition product is a very reactive material. Thus, as indicated above, hydrolysis can be made to takeplace to form dihydronaphthalene, or the addition product still in the ether solution can be treated with CO: and converted into sodium salts of dihydronaphthalene dicarboxylic acids, which can be isolated. The further reactions of this sodium naphthalene addition product are not, however, claimed in this application.

In carrying out these reactions. I'have found it to be of importance to have the surfaces of the sodium clean. Thus the solvent must be purified of such materials as will react with sodium and tend to form insoluble coatings thereon, under the conditions to be used, and the sodium should be protected from contact with such reactive materials from the time it is mechanically subdivided. Extreme fineness of sodium is not required although the rate will be dependent, among other things, on the extent of sodium surface, and this affords one means of controlling the rate. The naphthalene need not be of extreme purity. Technical flake naphthalene works quite satisfactorily. The complete absence of all sulfur compounds is-not essential as shown by the fact that dimethyl sulfide'can be used as an inert diluent solvent in the effective reaction medium for the reaction of sodium with naphthalene. The presence of free CO2 dissolved in the solvent is likely to interfere with the reaction of sodium with naphthalene starting because of coating the sodium.

On the other hand, when the reaction is well.

started, dry CO: can then be introduced and the carboxylation carried on simultaneously as long as care is taken that the rate is insuflicient to destroy completely all the green color of the sodium naphthalene compound, which will continue to be formed by the reaction of additional sodium. In this way the preparation of the sodium salts of the dicarboxy acids can be carried out simultaneously in a single vessel. In order to insure complete freedom from metallic sodium in the product, however, it is better to filter the green solution of the sodium naphthalene away from the unreacted sodium and treat it with CO2 in a separate vessel. This precipitates the sodium salts which can be filtered out and the solvent, together with unreacted naphthalene and a small amount of the sodium naphthalene compound returned to the first vessel. Such a process can be operated either as a batch processor continuously.

The concentration of naphthalene or its derivatives that can be used is limited only by its solubility. The reaction temperature can vary from at least C. to above the melting point of sodium, limited only by the stability of the combination of materials used and that of the product. The reactions in general are fast up to the solution of one gram atom of sodium per gram molecule of naphthalene in solution. In these reactions, both in the prior reaction with sodium and in the ,carboxylation, obviously pressures above atmospheric may be used if desired or necessary to confine the solvents at the temperatures found most optimum for the reaction.

The following examples are given by way of further illustration:

Example I c. c. of dimethyl ethylene glycol ether at room temperature were placed in a flask and-to this was added 19 gms. of flake naphthalene and then 5.8 gms. of clean, finely divided sodium. The reaction commenced immediately upon adding the sodium as was evidenced by the solution turning an intensely green color. This solution was agitated continuously for about fifteen minutes and then a slow stream of CO: wasintroduced while the agitation was continued; this stream of CO: was maintained at such rate that the green color of the solution was not com-' pletely discharged until the sodium had essentially all dissolved or reacted. Toward the end of two hours, the carboxylation was allowed to go to completion; the green color was completely discharged and in the vessel was a white slurry of sodium salts of dihydronaphthalene-dicarboxylic acids. On treatment of the salts with aquetained in varying amounts, amongst which the 1 :2 acid has been found to a considerable amount.

Example I! A solution of 128 gms. of naphthalene in approximately 900 c. c. of purified diethyl ethylene glycol ether was agitated in contact with 46 grams oi sodium in the form of chips, the solution being kept under a nitrogen atmosphere. The mixture was maintained at 24-26 C. and samples of the solution withdrawn at intervals for titrations of their sodium content; the sodium content of the solution is indicative of the extent of the reaction since the sodium is insoluble in the reactants. This was determined by first adding excess methanol to the sample to react with the addition compound and then titrating with standard acid. The results showed the presence of 5.2 gms. sodium per liter at the end of one hour, 18.2 gms. at the end of two-and-one-half hours, and 21.7 gms. at the end of twenty-four hours. The rate in either case can be varied by such factors as the extent of sodium surface, but it becomes almost negligible when one gram atom of sodium has dissolved for each molecule of naphthalene in solution.

Example III 11.6 gms. sodium and 39 gms. naphthalene were added to 375 c. c. glycol formal. The reaction started immediately. After fifteen minutes agitation, treatment with CO2 was begun as in Example I, and completed in two hours. 0

Example IV In order to demonstrate the ease of reaction of alkali metals with naphthalene and its homologues in a wide variety of polyether solvents a large number of experiments were carried out in a qualitative manner. A solution of naphthalene or its homologues in the ether was treated with the alkali metal preferably though not necessarily in contact with nitrogen instead of air, and the metal surface scraped under the solution if necessary to start reaction. The formation of the characteristic colored compound in solution tool: place readily at ordinary temperature.

Ethers tested in this manner for bringing about the reaction of sodium with naphthalene included the following: methylai: ethylene glycol diethers such as the methyl methyl, methyl ethyl. ethyl ethyl, methyl butyl, ethyl hutyl, butyl butyl. butyl lauryl: trimethvlene glycol dimethyl ether; glycerol trimethyl ether; glycerol dimethyl ethyl ether; methyl ortho iormate; ethyl ortho iormate; diethylene glycol methyl ethyl ether; formal oi the monomethyl ether of ethylene glycol; cyclic ethers such as dioxane, glycol formal, methyl glycerol formal; dimethylene pentaerythrite.

In a similar manner potassium was shown to react readily with naphthalene, alpha methyl naphthalene and beta methyl naphthalene in dimethyl glycol ether. Lithium was shown to react readily with naphthalene, with alpha methyl aosaaoa naphthalene and with beta methyl naphthalene in the same solvent; and sodium to react readily with alpha methyl naphthalene and with beta methyl naphthalene. v

I claim:

i. A method of ei'lecting the addition of sodium to naphthalene which comprises reacting the sodlum and naphthalene in a reaction medium comprising an amount of ethylene glycol methyl ethyl ether suillcient to promote the reaction.

2. A method of eflecting the addition of an alkali metal to an aromatic hydrocarbon of the group consisting of naphthalene and its homologues which comprises reacting the alkali metal and the hydrocarbon in a reaction medium comprising an amount of ethylene glycol methyl ethyl ether sumcient to promote the reaction.

NORMAN D. SCOTT. 

